Open your browser and enter the routers address into the address bar and hit enter. The router address can be found in the user manual and on the Negear support web page and sometimes on the bottom of the router itself. (192.168.1.1 or 192.168.0.1)
Once you hit enter it will bring up the routers log in page and you can enter in the routers default user name and password if you haven't changed it. The default user name and password can also be found in the same locations as the routers address.
Once in the routers internal settings go to the wireless section and in the wireless security sub-menu you will find your wireless security key and at this point you should write it down and keep it some place for future refference and/or you can change it if you want. But if there are other devices on the network then you will have to re-enter the new password if you do change it.